1. Field of the Invention
This invention relates to photosetting magnetic colloids to be suitably used to visualize the recorded pattern of magnetic discs, photomagnetic discs or to magnetic flaw detection.
2. Description of the Prior Art
Ferrofluid compositions have widely been used as a conventional medium for magnetic flaw detection. Such ferrofluids are used by applying them onto the surface of the article or parts to be inspected so as to detect whether and where exists any flaw or defect in the article or parts.
It is very difficult for a mere micrographic examination to find out such defect when fine cracks, scratches or foreign matter are located very close to the surface of the article.
Once a magnetic field is formed in the article to be inspected the magnetic field will become nonuniform at the location of a defect because the magnetic flux leaks at the location of such defect. If ferrofluid is applied to the surface of article to be inspected, the applied ferrofluid will be attracted to the portion where magnetic flux leaks and will swell to form a pattern corresponding to the configuration of the defect portion.
It is widely recognized that the finer the ferromagnetic particles, the greater the sensitivity of the ferrofluid and thus the accuracy of magnetic flat detection can also be improved.
Indeed, when the particle diameter of the ferromagnetic particles are decreased to submicron size or even to several tenth angstrom (.ANG.), the particles themselves cannot be observed by an optical microscope, but the region where any defect exists can be clearly observed, since the manner of the light beam reflection differs from that of the other portions where there is no swelling. Even if such defect cannot directly be observed through a microscope, the existence of such defect can be observed as a bright and dark image in the microphotograph.
However, since the conventional ferrofluid used in magnetic flaw detection was exactly a conventional fluid as previously described and is merely held at the portion being bound by the leaked magnetic flux, the fluid begins to flow as soon as the magnetic field applied to the article is removed. Naturally, the swelling of the fluid which indicates the pattern of the defect also disappears.
Accordingly, the defective region becomes unidentifiable as soon as the article to be inspected is removed from the magnetic field.
In view of the drawbacks mentioned above, it is desirable that a ferrofluid be formulated in which a pattern does not disappear once formed even if the article is removed from the magnetic field.
It is also desirable that this ferrofluid contain a photosetting resin or resins used as a carrier into which ferromagnetic particles can be stably dispersed.
The desired ferrofluid could be applied onto the surface of the article to be inspected so as to form a distribution pattern of the ferrofluid corresponding to the defective region of the article or to the magnetic flux pattern formed by the magnetic recording. Subsequently a beam of light having such a specific wave length that is able to set or harden the photosetting resin could be applied onto the surface so as to fix the defect pattern thus formed.
The desired ferrofluid would address the drawbacks encountered in the conventional ferrofluids. It is desirable to provide a ferrofluid which is able to fix and hold a pattern of the ferrofluid corresponding to the pattern of the magnetic flux formed by the defect in the article to be inspected.
The desired ferrofluid would be able to fix and hold the pattern of ferrofluid thus solving the problems of fixation, holding and observation of the pattern of the defect outside the applied magnetic field. However, since the desired ferrofluid would contain a carrier which in itself was a kind of photosetting resin, the swelled portion of the ferrofluid caused by the leaked magnetic field due to any defect in the article might be gentle in its inclination; giving rise to insufficient sharpness in the image of the photomicrograph taken for observation. Thus, it would be desirable to develop a ferrofluid and process for using the same which would obviate all such problems explained above and would provide such a high sensitive photosetting ferrofluid permitting not only fixation of the pattern of the ferrofluid corresponding to the article to be inspected but also to the taking of photomicrographs having very sharp contrast.